You can test the upstream oxygen sensor (commonly known as the O2 Sensor Bank 1 Sensor 1: O2S11) before replacing it... to make sure it's really bad, and in this article I'll show you how.
The most common symptom, of a failed O2 sensor, are the OBD II Codes P0131, P0133. What sucks is that the PCM may think they're bad when they're really not... so testing them makes a lot of sense.
Contents of this tutorial:
Important Suggestions And Tips
TIP 1: A scan tool with Live Data capability is a must to use the testing info in this article.
You don't need the Honda factory scan tool or an expensive professional technician level scan tool to follow the test procedures in this article, since a simple generic scan tool will do just fine (Don't have a scan tool? Need a scan tool? Check out my recommendation: Actron CP9580 Scan Tool).
TIP 2: The oxygen sensor test, I'm gonna' show you in this article, is an On Car Test, so you do not need to remove it to test it.
Symptoms Of A Bad Oxygen Sensor
The effects of a bad oxygen sensor can be very subtle since they usually do not cause serious drive-ability problems.
For the most part, you're able to drive your Honda normally... As if nothing were wrong (although not in all cases).
Here are the most common symptoms:
- The check engine light (CEL) will be illuminated on your instrument cluster.
- The diagnostic trouble codes lighting up the CEL usually are:
- P0131 Upstream Heated Oxygen Sensor (O2S11) Circuit Out Of Range Low Voltage (Bank 1).
- P0133 Upstream Heated Oxygen Sensor (O2S11) Circuit Slow Response (Bank 1).
- Really bad gas mileage.
- Won't pass state mandated emission testing (smog check).
Oxygen Sensor Basics
The oxygen sensor is tasked with the job of helping the PCM (Powertrain Control Module = Fuel Injection Computer) fine tune the amount of fuel that's being injected into the cylinders.
This fine-tuning helps to control emissions and improves gas mileage. How? By reporting if the Air Fuel Mixture is either Rich or Lean.
Rich means that the PCM is injecting too much fuel for the amount of available air entering the cylinder and Lean means that not enough fuel is being injected.
Here are some more specifics:
As the engine runs, the PCM is constantly injecting fuel. If it injects too much, the oxygen sensor reacts by producing a voltage above 0.500 Volts. Depending on how Rich the Air/Fuel Mixture, this voltage can go as high as 0.900 to 1.0 Volt.
As soon as the PCM sees this, it starts to inject less fuel.
As the PCM starts to inject less fuel, it may go too far and not inject enough. The resulting Lean condition will make the O2 sensor produce and report a voltage below 0.500 Volts. Depending on how Lean the air/fuel mixture is, the O2 Sensor's voltage can go as low as 0.050 to 0.100 Volts.
When the PCM sees these voltage numbers, it knows to inject more fuel.
This process (of adjusting the amount of fuel being injected) by the PCM, goes on the entire time the engine is running (and if the O2 sensor is working correctly).
All of these oxygen sensor voltages changes can be easily observed with a scan tool in Live Data mode, and this is how I'm gonna' show you how to test them.
A correctly working O2 sensor will produce a voltage that will switch between a Lean and Rich condition several times every few seconds. So, if the voltage output of the O2 sensor stays fixed (when testing it), the O2 sensor has failed.
To find out what are some of the most common symptoms of a failed oxygen sensor, take a look at the section: Symptoms Of A Bad Oxygen Sensor. OK, let's get testing.
O2 SENSOR TEST: Manually Inducing A Rich Condition
To test the oxygen sensor (O2S11), the very first thing you'll do is to induce a Rich condition.
This can easily be done by spraying a little carburetor cleaner into the engine while it's running. My preferred method is to spray carb spray into a vacuum hose.
Once the carb spray hits the engine cylinders, you'll get an instant Rich condition which will make the O2 sensor respond by producing its maximum voltage (0.900 Volts +) and you'll be able to see this on your scan tool (in Live Data mode).
Alright, this is what you'll need to do:
Start your vehicle and let it idle for about 15 minutes, since you need a warmed up engine to get the O2 sensor to activate. (Don't have a scan tool? Need a scan tool? Check out my recommendation: Actron CP9580 Scan Tool).
Connect your scan tool and get to its Live Data mode.
Once you're in Live Data mode, scroll down to the PID that's labeled O2S11. This PID will show you the oxygen sensor voltage activity.
What you should see, if the engine has been idling for about 15 minutes, are the voltage numbers of the O2 Sensor moving between 0.100 and 0.900 Volts constantly.
If the Voltage value stays fixed, don't worry about this yet, continue to the next step.
STEP 4 Continued in the next page...